Pinout and Signal Descriptions
M68HC12B Family Data Sheet, Rev. 9.1
Freescale Semiconductor
27
1.6.2.5 VFP (MC68HC912B32 and MC68HC912BC32 only)
VFP is the FLASH EEPROM programming voltage and supply voltage during normal operation for the
MC68HC912B32 and MC68HC912BC32 only.
1.6.3 Signal Descriptions
The MCU signals are described here and summarized in
Table 1-3.
1.6.3.1 XTAL and EXTAL
XTAL and EXTAL are the crystal driver and external clock input pins. They provide the interface for either
a crystal or a CMOS compatible clock to control the internal clock generator circuitry. Out of reset the
frequency applied to EXTAL is twice the desired E-clock rate. All the device clocks are derived from the
EXTAL input frequency.
XTAL is the crystal output. The XTAL pin must be left unterminated when an external CMOS compatible
clock input is connected to the EXTAL pin. The XTAL output is normally intended to drive only a crystal.
The XTAL output can be buffered with a high-impedance buffer to drive the EXTAL input of another
device.
NOTE
In all cases, take extra care in the circuit board layout around the oscillator
pins. Load capacitances shown in the oscillator circuits include all stray
oscillator circuits.
Table 1-2. Power and Ground Connection Summary
Mnemonic
Pin Number
Description
VDD
10, 47
Internal power and ground
VSS
11, 48
VDDX
31, 78
External power and ground supply to pin drivers
VSSX
30, 77
VDDA
59
Operating voltage and ground for the ATD; allows the supply
voltage to be bypassed independently
VSSA
60
VRH
49
Reference voltages for the analog-to-digital converter
VRL
50
VFP
69
Programming voltage for the FLASH EEPROM and required
supply for normal operation — MC68HC912B32 and
MC68HC912BC32 only.
Pin 69 is a no connect (NC) on the MC68HC12BE32 and
MC68HC12BC32.